Semiconductor light-emitting device

ABSTRACT

A semiconductor light-emitting device includes a lead frame, a semiconductor light-emitting element mounted on the top surface of the bonding region, and a case covering part of the lead frame. The bottom surface of the bonding region is exposed to the outside of the case. The lead frame includes a thin extension extending from the bonding region and having a top surface which is flush with the top surface of the bonding region. The thin extension has a bottom surface which is offset from the bottom surface of the bonding region toward the top surface of the bonding region.

This application is a Continuation of application Ser. No. 12/890,964,filed Sep. 27, 2010, which is a Division of application Ser. No.12/079,760, filed Mar. 28, 2008, which applications are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor light-emitting deviceprovided with a semiconductor light-emitting element.

2. Description of the Related Art

FIGS. 6 and 7 illustrate an example of conventional semiconductorlight-emitting device (see JP-A-2005-353914, for example). Theillustrated semiconductor light-emitting device X includes a lead frame91, an LED chip 92, a case 93, and a transparent resin 94. The leadframe 91 includes two strip portions, i.e., a relatively long portion 91a and a relatively short portion 91 b, as seen from FIG. 6. These twoportions, having the same width as seen from FIG. 7, are fitted into alower space in the case 93 in a manner such that the bottom surface ofthe lead frame 91 is exposed out of the case 93. The LED chip 92 servesas a light source of the semiconductor light-emitting device X, and isbonded to the longer strip portion 91 a of the lead frame 91. The LEDchip 92 is connected to the shorter strip portion 91 b of the lead frame91 via a wire 95. The light-emitting device X may be mounted on aprinted circuit board, for example.

In order to obtain stronger light emission from the semiconductorlight-emitting device X, it is required to apply greater electricalpower to the LED chip 92. Inevitably, the amount of heat generated bythe LED chip 92 is increased, and for maintaining the proper lightemission, the heat should be conducted from the longer strip portion 91a to the circuit board. One way to facilitate the heat conduction is tobroaden the strip portion 91 a (hence the lead frame 91) to which theLED chip 92 is attached.

While the width of the longer strip portion 91 a is to be increased, theoverall size of the case 93 may be unchanged so that the light-emittingdevice X is kept compact. In this case, the side walls of the case 93need to be made thinner to permit the size increase of the longer stripportion 91 a. This configuration, however, will weaken the frame-holdingforce of the case 93, which may allow the lead frame 91 to drop off fromthe case 93.

SUMMARY OF THE INVENTION

The present invention has been proposed under above-describedcircumstances, and thus an object of the present invention is to providea semiconductor light-emitting device that is compact and capable ofemitting bright light.

According to the present invention, there is provided a semiconductorlight-emitting device comprising: a lead frame including a bondingregion having a top surface and a bottom surface; a semiconductorlight-emitting element mounted on the top surface of the bonding region;and a case covering part of the lead frame. The bottom surface of thebonding region is exposed to an outside of the case. The lead frameincludes a thin extension extending from the bonding region and having atop surface and a bottom surface. The top surface of the thin extensionis flush with the top surface of the bonding region, while the bottomsurface of the thin extension is offset from the bottom surface of thebonding region toward the top surface of the bonding region.

Preferably, the semiconductor light-emitting device of the presentinvention may further comprise a thick extension extending from thebonding region and having a top surface and a bottom surface. The thickextension is arranged adjacent to the thin extension and is the same inthickness as the bonding region. The bottom surface of the thickextension is exposed to the outside of the case.

Other features and advantages will be apparent from the followingdescription with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating the principal portions of asemiconductor light-emitting device according to the present invention.

FIG. 2 is a bottom view illustrating the semiconductor light-emittingdevice shown in FIG. 1.

FIG. 3 is a sectional view taken along lines III-III in FIG. 1.

FIG. 4 is a sectional view taken along lines IV-IV in FIG. 1.

FIG. 5 is a sectional view taken along lines V-V in FIG. 1.

FIG. 6 is a sectional view illustrating a conventional semiconductorlight-emitting device.

FIG. 7 is a sectional view taken along lines VII-VII in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

FIGS. 1-5 illustrate a semiconductor light-emitting device according tothe present invention. The semiconductor light-emitting device Aincludes a lead frame 1, a light-emitting diode (LED) chip 2, a case 3,and a protection resin 4 that allows the passage of light emitted fromthe LED chip 2. The light-emitting device A is a small rectangularparallelepiped having a length of about 4 mm, a width of about 1 mm, anda height of about 0.6 mm. In FIG. 1, for convenience of explanation, theprotection resin 4 is not shown.

The lead frame 1 is made of Cu, Ni, or an alloy containing Cu and/or Ni.As shown in FIG. 2, the lead frame 1 is exposed out of the case 3 at itsbottom surface, and is divided into a longer primary portion and ashorter secondary portion. The primary portion includes a bonding region11, a plurality of thin extensions 12, and a plurality of thickextensions 13. In FIG. 1, the boundary between the bonding region 11 andthe extensions 12, 13 is indicated by double-dot broken lines.

The bonding region 11 is a strip-shaped region on part of which the LEDchip 2 is mounted. Each of the thin extensions 12 extends out from thebonding region 11, and has a thickness which is about half the thicknessof the bonding region 11, for example. As shown in FIG. 4, the topsurfaces of the thin extensions 12 are flush with the top surface of thebonding region 11. The bottom surfaces of the thin extensions 12 arepositioned higher than the bottom surface of the bonding potion 11, asviewed vertically in FIG. 4 (in other words, the bottom surfaces of thethin extensions 12 are offset toward the top surface of the bondingregion 11 from the bottom surface of the bonding region 11). The bottomsurfaces of the thin extensions 12 are covered by the case 3.

As shown in FIG. 5, each of the thick extensions 13 extends out from thebonding region 11, and has a thickness which is substantially the sameas the thickness of the bonding region 11. The top surfaces of the thickextensions 13 are flush with the top surface of the bonding region 11,and the bottom surfaces of the thick extensions 13 (which are flush withthe bottom surface of the bonding region 11) are exposed to the outsideof the case 3. As shown in FIGS. 1 and 2, the thin extensions 12 and thethick extensions 13 are arranged alternatively in the longitudinaldirection of the lead frame 1.

The LED chip 2 as a light source of the light-emitting device A isconfigured to emit light of a predetermined wavelength. The LED chip 2is made of a semiconductor material such as GaN, for example, and emitsblue light, green light, or red light by the recombination of electronsand holes at an active layer sandwiched by an n-type semiconductor layerand a p-type semiconductor layer. The LED chip 2 is connected to theshorter portion of the lead frame 1 via a wire 5.

The case 3 is made of a white resin, for example, and is a generallyrectangular frame. As shown in FIGS. 3-5, the inner surfaces of the case3 serve as a reflector 3 a that tapers downward. The reflector 3 aupwardly reflects light which is emitted laterally from the LED chip 2.As shown in FIG. 4, the case 3 is held in unreleasable engagement withthe thin extensions 12. Further, as shown in FIG. 2, the case 3 is inmesh with the thin extensions 12 and the thick extensions 13.

The protection resin 4 is made of a transparent or transparent epoxyresin, for example, filled in a space defined by the case 3. Theprotection resin 4 covers the LED chip 2, and while protecting the LEDchip 2.

Next, the functions of the semiconductor light device A will bedescribed below.

As described above, the case 3 is held in unreleasable engagement withthe thin extensions 12. Thus, the lead frame 1 is reliably held by thecase 3, to be prevented from dropping off from the case 3. As a result,though the light-emitting device A has a very small width (about 1 mm),the lead frame 1 is exposed out of the case 3 in a relatively largearea, as seen from FIG. 2. Therefore, heat can be efficiently conductedfrom the LED chip 2 to a printed circuit board, for example, whichcontributes to attaining light emission of desired intensity.

As described above, the thin extensions 12 and the thick extensions 13are arranged to alternate with each other, and the bottom surfaces ofthe thick extensions 13 are exposed to the outside of the case 3, asshown in FIG. 2. In this manner, the exposed area of the lead frame 1can be increased. Advantageously, this facilitates the heat dissipationfrom the led chip 2.

The invention claimed is:
 1. A semiconductor device comprising: a firstlead frame including a bonding region provided with an upper surface anda lower surface; a semiconductor element mounted on the upper surface ofthe bonding region; and a case covering part of the first lead frame;wherein the first lead frame includes thin extensions extending from thebonding region in a width direction of the first lead frame, each of thethin extensions being smaller in thickness than the bonding region, andthe lower surface of the bonding region is exposed from a bottom surfaceof the case.
 2. The semiconductor device according to claim 1, whereinthe first lead frame is formed with a first recess located betweenadjacent ones of the thin extensions, the first recess being indented inthe width direction relative to the adjacent ones of the thinextensions.
 3. The semiconductor device according to claim 1, whereinthe first lead frame includes a thick extension greater in thicknessthan the thin extensions, the thick extension being located betweenadjacent ones of the thin extensions.
 4. The semiconductor deviceaccording to claim 1, wherein the thin extensions are disposed atregular intervals.
 5. The semiconductor device according to claim 1,further comprising: a second lead frame including a wire bonding region;and a wire for connecting the wire bonding region and the semiconductorelement to each other; wherein the case covers the second lead frame ina manner allowing the wire bonding region to be exposed to an outside ofthe case, wherein the second lead frame includes a second thin extensionextending from the wire bonding region, the second thin extension beingsmaller in thickness than the wire bonding region.
 6. The semiconductordevice according to claim 5, wherein the second lead frame includes aterminal at an end thereof opposite to the first lead frame, and thesecond lead frame is formed with a second recess located between theterminal and the second thin extension, the second recess being indentedin the width direction relative to the second thin extension.
 7. Thesemiconductor device according to claim 5, wherein the width directionis perpendicular to a separation direction in which the first lead frameand the second lead frame are spaced apart from each other.
 8. Thesemiconductor device according to claim 7, wherein the thin extensionsare aligned in the separation direction.
 9. The semiconductor deviceaccording to claim 1, wherein the bottom surface of the case and thelower surface of the bonding region are flush with each other.
 10. Thesemiconductor device according to claim 1, wherein each of the thinextensions includes an end that is spaced from the bonding region in thewidth direction and embedded in the case.
 11. The semiconductor deviceaccording to claim 2, wherein the first lead frame includes a terminalprotruding from the case in a separation direction that is perpendicularto the width direction, the first lead frame is formed with anadditional recess facing the first recess in the width direction, and adistance between the first recess and the additional recess is equal toa size of the terminal of the first lead frame in the width direction.12. The semiconductor device according to claim 1, wherein each of thethin extensions includes a lower portion parallel to the upper surfaceof the bonding region.
 13. The semiconductor device according to claim1, wherein the first lead frame includes an upright portion connected toboth the lower surface of the bonding region and one of the thinextensions, the upright portion being perpendicular to the upper surfaceof the bonding region.
 14. The semiconductor device according to claim2, wherein the first recess corresponds in location to the semiconductorelement along a longitudinal direction of the first lead frame.